PBAP: Synchronize call to CloseService when Service is Destroyed

Synchornize call to CloseService when onDestroy is called for BluetoothPBapService
otherwise we might have timing issue, when closeService is being processed due to BT
being turned off and at same time we get call to onDestroy. So synchronize the calls
to prevent crash due to concurrent access of some variables which are being freed.

CRs-Fixed: 1026855
Change-Id: I8da1ec384ba787c6047c41c4db9d6be633864e17